A leading authority on Schmallenberg virus (SBV) is warning farm vets to be prepared for the possibility of a springtime spike in cases of abnormal births and deformities in sheep and cattle.

Rachael Tarlinton, a lecturer in veterinary cellular microbiology at The University of Nottingham, was reacting to reports of positive tests for SBV in bulk milk in dairy herds in Wales and the west of England. Positive blood samples from heifers and lambs have also been reported.

Virus circulation

Schmallenberg. Image courtesy Animal and Plant Health Agency.
“The worst deformities to newborns happened when their mothers were infected mid-gestation.” Image courtesy APHA.

Dr Tarlinton said SBV hadn’t been circulating in the UK for some time, but suggested that was a mixed blessing. She explained: “After the initial outbreak, when we got to about 2013, probably 70% of the national sheep flock and cattle herd had seroconverted and had become immune.

“What’s happened since then is the virus hasn’t circulated very much. A recent study conducted in the southern UK suggests the virus hadn’t circulated at all in 2014 and 2015. What that means is animals born since 2013 haven’t been exposed to SBV, so aren’t immune. Overall, quite a large percentage of our national flock and herd is naïve to the virus – particularly the sheep, as a lot of those original, immune animals will have been culled by now.”

The exact extent of the naïvety is unknown as funding had not been available for systematic follow-up work, she said.

Vigilance

Dr Tarlinton suggested the severity of an outbreak may depend on when livestock had mated in terms of timing when the virus went through. She said the worst deformities to newborns happened when their mothers were infected mid-gestation.

She added the only positive was the earliest lambing flocks were already beginning to give birth and they hadn’t seen lots of reports of deformities yet.

A further complication was no vaccines against SBV were available. She said at least three had been registered, but all had been withdrawn as sales had been too low to be commercially sustainable.

  • Read the full story in the 16 January issue of Veterinary Times.
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